Explosive compositions



United States Patent EXPLOSIVE coMPosmoNs James Taylor, London, England,and Thomas James Reid, Ardrossan, Scotland, assignors to ImperialChemical Industries Limited, a corporation of Great Britain No Drawing.Application November 2, 1953 Serial No. 389,887

Claims priority, application Great Britain November 1 9, 1952 Claims.(Cl. 52-7) The present invention relates to an improvement in theproduction of safety ammonium nitrate blasting explosive powders such asare used in fiery or dusty mines and of the kind wherein. thesensitizing explosive ingredient is trinitrotoluene and the flamequenching ingredient comprises sodium chloride.

An example of such a safety ammonium nitrateexplo- 2,839,374- PatentedJune 1'1, 195 8 ice only gentle mechanicallmixing action and without theexercise of appreciable pressure.

Hitherto in the manufacture of ammonium nitrate trinitrotolueneexplosives containing sodium I chloride or other ingredients, theingredients have all been ground togethen We have now found that thefine state of division of the sodium chloride particles resulting fromtheir comminution in the grinding operation greatly enhances the sive isDouglas powder, which is r'nade by grinding to-' g V trinitrotoluene andsodium chloride wherein the ammonium nitrate and the trinitrotolueneconsist of fine par:

gether trinitrotoluene, ammonium nitrate and sodium chloridesubstantially in the proportions 15:69:16 by weight and which has apower equivalent to 65% of that of blasting gelatine as determined inthe ballistic mortar, and which just passes a Home Ofiice gallery testin which the cartridge is fired unstemmed from a steel gun or cannonwith a 47 inch bore into a gallery containing a ture of 9% by'volume ofmethane in air, The velocity of detonation of Douglas .powde'r ,is 7about. 3,000 metres/second. However, the improvement in safetycharacteristics exhibited by more modern explosives and especiallysheathed nitroglycerine explosives and the increasingly high safetycharacteristics expected in recent years have resulted in attempts tomake safer explosives based on trinitrotolueneand ammonium nitrate byincreasing the sodium chloride content, but hitherto because of theresulting diminution insensitivity to propagation it has not beenpracticable to increase the'sodium chloride content beyond approximatelyas in the explosive Gathurs't powder which contains 15% trinitrotoluene,60% ammonium nitrate and 25% sodium chloride by weight and has a powerequivalent to 53% of that of blasting gelatine and a velocity ofdetonation of about 2,800 metres/second. In order to circumvent thisditficulty there have also been introduced wrapped cartridges ofexplosives containing ammoniumnitrate, trinitrotoluene and'sodiumchloridetsheathed with a layer of sodiumbicarbonate on theirlongitudinal surfaces between the wrapper and an outer wrapper, thesodium bicarbonate layer serving to assist in preventing ignition of'thefiredamp atmosphere and of reducing the power developed by thecartridges without substantially reducing their sensitiveness topropagation. Sheathed explosives have, however, the disadvantage thatthey necessitate the provisionof wider boreholes and their manufactureis troublesome owing to the necessity forpreventing the sheathingmaterial? from covering the end surfaces of the cartridges and thenecessity of an extra wrapper, apart-from the fact that;

accidental damage to the sheath may result in a loss of its safetyadvantageg f The manufacture of ammonium nitrate explosive com-vpositions in which the sensitizing ingredient is trinitrotoluene differsfronithemanufactureof those -in which the sensitizingexplosiveingredient is a liquid explosive nitric ester in that in theformer grinding is :necessary desensitizing effect of sodium chloridecontaining it.-

In general'the object of the present invention is to pro vide ammoniumnitrate blasting explosives of the kind containing trinitrotoluene andsodium chloride which will have improved safety. a

- According to the present invention asafety ammonium nitrate blastingexplosive powder of the kind comprising ditions in a gallery testexplosives according to the invention containing this amount of finesodium chloride give better results than those containing no finesat:all, and are equally satisfactory acannon I, V, I It is well knownthat for safety explosive compositions consisting of a mixture oftrinitrotoluene, ammoniumv nitrate and sodium chloride not to give olfpoisonous fumes on initiation, that these compositions should have acalculated oxygen balance between 0.5 and +3 gms./ gms. of thecomposition. V j It is also often desirable to include in suchcompositions up to 4.5% of fibre in order to lower the bulk-density ofthe composition and to restore oxygen balance in explosives where thetrinitrotoluene content is reduced to give enhanced safety From thestipulated oxygen of 0.5 to +3 gms. oxygen per 100 gms. of thecomposition it can be deduced that the percentage by weight oftrinitrotoluene must be between 5 and 15.5 and the percentage by weightof ammonium nitrate must be between 40 and 60 (if no other oxygenproducing salt is included) and having regard to the total quantity offlame quenching ingredients of'a sheathed explosive of thenon-nitroglycerine, trinitrotol in the test in which theyare fired fromuene, ammonium nitrate type it can be assumed that the sodium chloridecontent for at least the same degree of safety should beat least 30%. Vi j Furthermore, it has been experimentally ascertained thatammoniumnitrate compositions of the aforesaid kind having at least 30% sodiumchloride must have a velocity 1 metre long made from l% inch diametercartridges of,

,. trinitrotoluene and sodium chloride'equiyaient in safety to on theexplosive.

sensitiveness for any desired degree of o sheathed Douglas powder, sothat 4 ozs. of the explosive when fired freely suspended in a gallerytest should fail to ignite a 9% by volume methane-air mixture, at least35% of sodium chloride should be included.

More particularly the object of the present invention is to provideammonium nitrate blasting explosives of. the kind containingtrinitrotoluene and at least 35% sodium chloride which will have avelocity of detonation of at least 2,300 metres/ second and not morethan 2,900 metres/second.

Said ammonium nitrate blasting explosives which have a velocity ofdetonation less than 2,300 metres/second are less sensitive than isusually desirable for commercial purposes, while those which have avelocity of detonation greater than 2,900 metres/second have an adverseefiect on the suspended gallery test.

More particularly, according to the present invention a safety ammoniumnitrate blasting explosive powder of the kind comprising trinitrotolueneand sodium chloride wherein the ammonium nitrate and the trinitrotolueneconsist of fine particles in intimate admixture is characterized in thatthe amount of sodium chloride is at least 35% by weight on the explosivepowder and in that such portion of the sodium chloride is retainable ona 120 B. S. S. sieve that the explosive powder has a velocity of atleast 2,300 metres/second and not more than 2,900 metres/ second.

For example, for a composition containing 35% sodium chloride it isdesirable to have at least 10% of sodium chloride on the explosivepowder retainable on said sieve; and for a composition containing 40%sodium chloride it is desirable to have at least 17.5% of sodiumchloride on the explosive retainable on said sieve.

It is to be understood that if for example sodium nitrate is includedless than 35% sodium chloride may give the desired degree of safety.

Preferably the grist is such that all of the sodium chloride passesa 16B. S. S, sieve in order to prevent segregation in transport.

By limiting the amount of the sodium chloride ground with thetrinitrotoluene and the ammonium nitrate or otherwise introduced intothe final explosive mixture to a division fine enough to pass a 120 B.S. S. sieve to not more than 25% of the weight of the final explosivemixture there may be obtained explosives containing from 30 to 60%sodium chloride and from to 12% trinitrotoluene, the remainderconsisting mainly of ammonium nitrate. If necessary sufficient of anoxidizing salt of a metal, e.'g. sodium nitrate and if desired alsonon-explosive solids in small proportions to give a satisfactory oxygenbalance may also be included, these resulting explosives havingsatisfactory initiation and propagation sensitiveness and having bettersafety characteristics than any of the known unsheathed ammoniumnitrate, trinitrotoluene, sodium chloride explosives.

Although the whole amount of the sodium chloride present in theexplosive composition may be of a grist too coarse to pass a 120 B. S.S. sieve, it is preferred that at least of the sodium chloride in thecomposition should be of a finer grist since under freely suspendedfiring conditions in a gallery test explosives according to theinvention containing this amount of fine sodium chloride give betterresults than those containing no fines at all, and are equallysatisfactory in the test in which they are fired from the cannon.

A process for the production of a safety ammonium nitrate blastingexplosive powder according to the present invention comprises grindingtogether trinitrotoluene and ammonium nitrate in known manner andthereafter lightly mixing into the milled mixture thus produced. sodiumchloride at least a'portion of which is retainable on a 120 B. S. S.sieve.

In putting the invention into efiect the trinitrotoluene and theammonium nitrate may be first ground in known manner, for example in anedge runner mill in the absence of sodium chloride and thereafter thesodium chloride, which may be wholly or partly of grist too coarsetopass a 120 B. S. S. sieve, may then be lightly mixed with the milledmixture without further grinding, for instance by transferring the saidmixture to an Atlas (registered trademark) mixer and working in thesodium chloride after the fashion employed in incorporating theingredients of explosives containing liquid explosive nitric esters, oralternatively if an edge runner mill has been used for milling theammonium nitrate and trinitrotoluene by working in the salt with theplows alone after raising the rolls clear of the mixture.

When it is desired that some of the sodium chloride in the finalexplosive should be fine enough to pass a 120 B. S. S. sieve, thatportion of the sodium chloride added in any desired state of divisionmay be ground with the trinitrotolu'ene and ammonium nitrate in theusual way, the portion too coarse to pass the 120 B. S. S. sieve beingthereafter lightly mixed in as such without milling. Another method isto mill the ammonium nitrate and trinitrotoluene with or without somesodium chloride in known manner and then introduce into the mill aquantity of sodium chloride having a grist size so that all is retainedby a 120 B. S. S. sieve and continue to mill for the short time untilmixing is completed and so that the main portion of the sodium chloridein the resulting composition still has a grist size which is retained ona 120 B. S. S. sieve.

The blasting explosives according to the invention retain theirsensitiveness, i. e. their firing properties for a period of at least 6months.

The following tables embody experimental data which indicate theproperties of compositions consisting of sodium chloride in admixturewith mixtures of trinitrotoluene and ammonium nitrate in a ratio of18.2: 81.8.

A positive sign indicates that the gas tests (suspended test and guntest) have been passed with respect to safety, a negative sign indicatesthat the gas test'has not been passed with respect to safety.

TABLE 1 Grist size of sodium chloride Power (per- Retained on cent 120B. S. S. Sodium ehlo- Blasting sieve .Veloeity oi safety in ridecontent, Gelatine) detonation gas percent Experi- Finely (m./sec.)mentally Passes 16 milled determined B. S. S. (parts) sieve, retained by60 B. S. S. sieve (parts) 1 Fails to propagate.

cassava TABLE 2 Grist size ol'sodium" chloride Sodium chlo- Power, per-Velocity oi ride content, cent Passes 60 detonation Safety in percentB/G B. S. 8. Final (m./sce gas sieve, remills tained by (parts) 120 B.S. S. sieve (parts) 28 7 2, 700 as 2,900 4o a9 20" 2,300

1 Falls to propagate.

Example I In an edge runner mill set for close grinding there are groundtogether 11.9 parts flake trinitrotoluene 'and 53.1 parts ammoniumnitrate having a fine surface deposit of the ammonium salt oftrisulphonated pararosaniline amounting to 0.1% of its weight, thegrinding being continued for minutes by which time substantially thewhole mixture is fine enough to pass a 150. B. S. S. sieve. Furthergrinding has no beneficial eflfects on its sensitiveness. After thegrinding is stopped the wheels are raised free of the mixture, intowhich there are worked by means of the plows 35 parts sodium chloridehaving a grist size so that all of it passes a 60 B. S. S. sieve andonly 58% passes a 120 B. S. S. sieve.

The resulting explosive has a velocity of detonation of 2,400metres/second, is sensitive to a No. 3 commercial fulminate detonatorand in the form of a 1.25 inch cartridge 3 inches long communicatesdetonation to a similar spaced 1 inch end to end from it. Its power is43% of that of blasting gelatine and it has a density of 1.15 gms./ml.at 20 lbs/sq. in. 6 ozs. when fired freely suspended in a gallery testfail to ignite ,a 9% by volume methane-air mixture.

A explosive of a similar composition but containing 35% sodium chloridein a finely divided form has a velocity of detonation of 2100metres/second, is not sensitive to a No. 3 commercial fulminatedetonator, and in the form of a 1.25 inch cartridge 3 inches long,communicates detonation to a similar cartridge spaced 0.5 inch end toend from it. 5 ozs. when fired freely suspended in the gallery test failto ignite a 9% by volume methaneair mixture.

Example 2 The wheels of the mill are then raised free of the mixture,

and 29 parts sodium chloride, having a grist size so that all of itpasses a 60 B. S. S. sieve and is retained on a 120 B. S. S. sieve, areworked into the mixture by means of the plows.

The resulting explosive has a velocity of detonation of 2600metres/second, is sensitive to a No. 3 commercial 1 fulminate detonator,and in the form of a 1.25 inch diam eter cartridge 3 inches long,communicates detonation to a similar cartridge spaced 1 inch end to endfrom it. Its power is 41% of that of blasting gelatine and it has adensity of 1.15 gms./ml. at 20 lbs/sq. in. 5 ozs. when fired freelysuspended in a gallery test fail to ignite a 9% i I by volumemethane-air mixture.

An explosive of similar composition containing 37% 15 5' long, fails' tocommunicate detonation to a similar cartridge spaced 0.5 inch end to endfrom it. 6 am. when fired freely suspended in the gallery test fail toignite a 9% by volume methane-air mixture. 7 I

Example 3 11 parts of trinitrotoluene are milled with'llparts ofammonium nitrate for 10 minutes as in Example 2.; 38 parts ammoniumnitrate are added and the mixture milled for a further 20 minutes: Thewheels of the mill are raised free of the mixture and. 40 parts sodium.chloride having a grist size so that all of it passes a 60 B. S. S.sieve and-is retained on a B. S. S. sieve are worked into the mixture bymeans of the plows.

The resulting explosive has a velocity of detonation of 2700metres/second, is sensitive to a No. 3 commercial fulminate detonator,and in the form of a 1.25 inch diameter cartridge 3 inches long,communicates detonation to a similar cartridge 1.5 inches end to endfrom it. Its power is 39% blasting gelatine and it has a density 'of1.15 gms./ml. at 20 lbs/sq. in. 502s. when fired freely suspended in agallery test failed to ignite a 9% by volume methane-air mixture.

An explosive of similar composition containing 40% sodium chloride in afinely milled state fails to propagate.

Example 4 11 parts of trinitrotoluene and 11 parts of ammonium nitrateare milled for 10 minutes. 38 parts ammonium nitrate and 20 parts sodiumchloride are added andthe mixture milled for a further 20 minutes. 20parts sodium chloride having a grist size so that all of it passes a 16B. S. S. sieve and is retained on a 60 B. S. S. sieve, are added andmilling continued for a further 3 minutes by which time mixing iscompleted and little comminution of the sodium chloride has taken place.

The resulting explosive has a velocity of detonation of 2400metres/second, is sensitive to a No. 3 commercial fulminate detouatorand in the form of a 1.25 inch diameter cartridge 3 inches longcommunicates detonation to a similar cartridge spaced 1 inch end to endfrom it. Its power is 39% blasting gelatine and it has a density of 1.15gms./ml. at 20 lbs./sq. in. 6 ozs. when'fired freely suspended in thegallery test fail to ignite a 9% by volume methane-air mixture.

An explosive of similar composition containing 40% sodium chloride infinely divided form fails to propagate.

Example 5 5.6 parts of trinitrotoluene and 5.6 parts ammonium nitrateare milled for 10 minutes in an edge runner mill. 48.9 parts ammoniumnitrate and 16.4 parts sodium chloride are added and milled for afurther 20 ininutes.-

The resulting explosive has a velocity of detonation of.

2600 metres/second, issensitive to a No. 2 commercial fulminatedetonator and in the form of a 1.25 inch di-- ameter cartridge 3 incheslong communicates detonation to a similar cartridge spaced 1 inch end toend from it. Its power is 41% of that of blasting gelatine and it has adensity of 0.98 gm./ml. at 20 lbs/sq. in. 6 ozs. when fired freelysuspended in the gallery test fail to ignite a 9% by volume methane-airmixture.

An explosive of similar composition containing 36.4 v parts sodiumchloride in a finely divided form has a velocit-y of detonation 2100metres/seeoiimsis' not sensitive to a No.7 3 commercial fu'lminatedetonator and ;ii1'.-the fornrof a 1125: inch cartridge 3" inches longcomin'uni eatesdetonati'on to a similar cartridge spaced =5 inchond" toend from'it. 6 ozs. when fired freely suspended in the gallery test.fail to ignite a 9% by volume methane-air mixture.

What we claim is:

1. A safety ammonium nitrate blasting explosive powder consistingessentially of about to 12% by weight trinitrotoluene, about 28 to 65%by weight ammonium nitrate, and greater than 35% by Weight sodiumchloride, wherein the ammonium nitrate and =trinitrotoluene cohsi st offine particles in intimate'admixture and wherein'atleast 'by weight ofthe sodium chloride is retainable on a 120 B. S. S. sieze and not morethan by weightof 'the sodium chloride passes a B; S. S.

sieve.

powder as cl-aimed in 'claim 1 wherein all of the sodium chloride passesa 16 BS. S. sieve.

References Cited in the file of this patent UNITED STATES PATENTS2,613,146 Lowe Oct. 7, 1952

1. A SAFETY AMMONIUM NITRATE BLASTING EXPLOSIVE POWDER CONSISTINGESSENTIALLY OF ABOUT 5 TO 12% BY WEIGHT TRINITROTOLUNE, ABOUT 28 TO 65%BY WEIGHT AMMONIUM WHEREIN THE AMMONIUM NITRATE AND TRINITROTOLUENECONSIST OF FINE PARTICLES IN INTIMATE ADMIXTURE AND WHEREIN AT LEAST 10%BY WEIGHT OF THE SODIUM CHLORIDE IS RETAINABLE ON A 120 B. S. S. SIEZEAND NOT MORE THAN 25% BY WEIGHT OF THE SODIUM CHLORIDE PASSES A 120 B.S. S. SIEVE.